Yes, I agree - they should.
But we can't force anyone.
Anyway, this might only be loosely related to the person actually "hating" your map .. I know of a number of people (myself included) that regularly re-evaluate nodes through their own vote.
If I see a node that has a rating I don't think it deserves I will modify my own vote to compensate.
And - it could also just be that even though the person thought your map was terrible (which I don't) he/she might not want to have posted to not hurt your feelings. It can sometimes be hard to keep criticism constructive or even free of abuse .. so .. sometimes .. better not to say anything out loud but just leave your opinion anonymously in the vote. (see quin's post)